A typical freight train includes one or more locomotives, a plurality of railcars and a pneumatic trainline referred to as the brake pipe. The brake pipe consists of a series of individual pipe lengths interconnected to each other. One pipe length secured to the underside of each railcar interconnects to another such pipe length via a flexible coupler situated between each railcar. The brake pipe supplies the pressurized air that is required by the brake control system to charge the various reservoirs and operate the air brake equipment on each railcar in the freight train.
A train operator situated in the lead locomotive can manipulate a brake handle to apply and release the brakes on the railcars as desired. The brake handle can be moved from and in between a release position at one extreme in which brake pipe pressure is maximum and the brakes are completely released to an emergency position at another extreme in which brake pipe pressure is minimal and the brakes are fully applied. The brake handle positions thus include brake release, minimum service brake application, full service brake application and emergency brake application. When the brakes are released, the reservoirs and the brake pipe are generally charged to the same pressure: typically 90 psi on a freight train and 110 psi on a passenger train. When the brakes are applied, the pressure in the brake pipe is reduced via a valve located in the lead locomotive. The exact amount by which the pressure is reduced depends into which of the application positions the brake handle is placed. It is this pressure reduction that signals the brake control valve on each railcar to supply pressurized air from the appropriate reservoir(s) to the brake cylinders. The brake cylinders convert this pressure to the mechanical force which the brake shoes apply to slow or stop the rotation of the wheels on the railcar. Assuming the brake signal is successfully communicated throughout the train, the brakes of all railcars in the train respond in generally the same manner.
The brake equipment on each railcar of a freight train typically includes one or more brake cylinders, an emergency air reservoir, an auxiliary air reservoir and a conventional pneumatic brake control system such as an "ABD" or similar type control valve. Each railcar may also include empty and load freight brake equipment such as a P-1 Load Proportional Valve and an S-1 Load Sensor Valve both of which are made by the Westinghouse Air Brake Company (WABCO) and are known in the brake control art.
FIG. 1a illustrates a schematic diagram of an ABD type pneumatic brake control valve. This control valve includes a service portion and an emergency portion typically mounted on opposite sides of a pipe bracket. It should be noted that there exists at least one other type of pipe bracket on which the service and emergency portions are mounted on the same side. Whether dealing with the dual sided or single sided variety, the pipe bracket features a number of internal passages and several ports. Each port connects to one of the interconnecting pipes from the railcar such as those leading to the brake pipe, the brake cylinder, the emergency reservoir and the auxiliary reservoir. It is through these ports and internal passages of the pipe bracket that the relevant portions of the control valve communicate fluidly with the pneumatic piping on the railcar.
The service and emergency portions of the pneumatic control valve operate according to principles well known in the railroad industry. The service portion of the control valve performs several functions including (1) controlling the flow of air from the auxiliary reservoir to the brake cylinder during a service brake application, (2) controlling the recharging of the auxiliary and emergency reservoirs, and (3) controlling the exhausting of the brake cylinder when the brakes are released. The emergency portion of the control valve controls, among other things, the flow of air from both reservoirs to the brake cylinder during an emergency brake application.
The American Association of Railroads (A.A.R.) has issued specification S-486-91 detailing the basic test procedures that must be performed periodically on the brake equipment of every railcar. It requires that the brake equipment be charged and tested for leaks. There exists a standard A.A.R. test device that can be used to perform such testing, but it is rather complicated and requires interpretation by a very skilled user to identify problems with the brake equipment. Accordingly, in U.S. application Ser. No. 08/365,815, WABCO has described and claimed an Automated Single Car Tester that can perform the requisite tests more reliably and quickly than the standard A.A.R. Test device. This copending application is assigned to the assignee of the present invention, and its teachings are incorporated into this document by reference.
Among other functions, the Automated Single Car Tester is used to measure the pressure at various points within the brake control system of the railcar. The single sided pipe bracket has a receiver assembly mounted to same side of the pipe bracket to which the service and emergency portions of the control valve mount. This receiver assembly provides the Automated Single Car Tester with quick and direct access to certain internal passageways of the pipe bracket and ultimately the pneumatic pipes and reservoirs whose pressure must be tested. Specifically, through the receiver assembly, the Automated Single Car Tester can measure pressure within the brake cylinder, the brake pipe, the emergency reservoir and the auxiliary reservoir. The dual sided pipe bracket, however, has its ports located on its rear side. Consequently, it is quite difficult to access the ports and the pipes that connect to them. Therefore, for railcars equipped with the dual sided pipe bracket, the Automated Single Car Tester is used in conjunction with a combination access and receiver assembly. This access plate portion of the assembly is typically connected between the pipe bracket and the service portion of the control valve as shown in FIGS. 1a and 1b. The receiver portion is assembled as shown in FIG. 1d. Connected to form the combined assembly as shown in FIG. 1b, the receiver portion together with the access plate provide access to the internal passageways of the pipe bracket. For railcars equipped with the dual sided pipe bracket, the combined assembly is the part through which the Automated Single Car Tester can measure the pressure within the brake cylinder, the brake pipe, the emergency reservoir and the auxiliary reservoir.
As will be apparent from the ensuing description and claims, the receiver portion and the receiver assembly of the two aforementioned pipe brackets are identical except in respects immaterial to the present invention. It is for this reason that the terms "receiver assembly" and "receiver portion" shall hereinafter be used interchangeably.
As shown in FIG. 1d, the receiver assembly includes a cover, a receiver body and four check valves housed in bores defined in the receiver body. Each check valve basically includes a shaped insert made of rubber or other suitable sealing material, a carrier that holds the shaped insert and a spring. A gasket and typically a filter are also used with each check valve. Consequently, each check valve is normally compressed against a check valve seat formed at the top of its bore. When the receiver assembly is mounted to the control valve, the check valves, at the head of the receiver body, are accessible by removal of the cover. Each check valve serves as an access port through which to access the pressure held in one of the following devices: the brake cylinder, the brake pipe and the emergency and auxiliary reservoirs. Even with the cover removed, each check valve acts as a seal that prevents leakage of the air under pressure.
The Automated Single Car Tester includes a pneumatic connector designed to mate with the head of the receiver body and thereby to each of the four access ports. By moving each check valve away from its check valve seat, the tester can charge and measure the pressure within the brake cylinder, the brake pipe, the emergency reservoir and/or the auxiliary reservoir.
The A.A.R. has proposed that each railcar of a freight train be provided with a mechanism that would allow the pressure within the brake cylinder to be read quickly. At present, the A.A.R. is considering whether to issue a specification requiring that a commercially available quick connect type fitting be used to access the pressure within the brake cylinder. The disadvantage of such a fitting, however, is that it provides only a single seal with which to contain the pressure to be measured. That is, while such a fitting is not being used to access the pressure, it offers only one seal to prevent leakage of the pressure that it is supposed to contain. Unless the fitting is routinely covered to protect the seal when the fitting is not being used to access the brake cylinder pressure, the seal is exposed to dust, dirt and/or other potential contaminants. It is, of course, important that such a fitting prevent leakage of pressure from the brake cylinder otherwise operation of the brakes may be adversely affected.
It should be noted that the foregoing background information is provided to assist the reader in understanding the instant invention. Accordingly, any terms used herein are not intended to be limited to any particular narrow interpretation unless specifically stated otherwise in this document.